Because of the well-known and clearly established activity of 1.alpha.-hydroxyvitamin D compounds in regulating calcium and phosphate homeostasis in the animal or human, there has been interest in the preparation of the natural metabolites and in the discovery of analogs with useful biological properties. This has led to the preparation of a variety of compounds exhibiting biological activity (for examples, see DeLuca et al., Topics in Current Chem., vol. 83, p. 1 (1979); Ann. Rev. Biochem. 52, 411 (1983); Yakhimovich, Russian Chem. Rev. 49, 371 (1980)). Interest in such compounds in continuing especially now that it has been recognized that in addition to their classical function as regulators of calcium homeostasis, certain vitamin D derivatives, specifically, 1.alpha.,25-dihydroxyvitamin D.sub.3 and 1.alpha.-hydroxyvitamin D.sub.3, also affect cellular differentiation processes and are capable of inhibiting the growth and proliferation of certain leukemic cells [Suda et al., U.S. Pat. No. 4,391,802; Suda et al. Proc. Natl. Acad. USA 80, 201 (1983); Reitsma et al., Nature, 306, 492-494 (1983)].
Most of the known vitamin D metabolites and analogs are derivatives of the vitamin D.sub.3 series, i.e. they possess saturated steroid side chains. Side chain unsaturated vitamin D compounds are, however, also known, namely certain hydroxyderivaties of vitamin D.sub.2 such as 25-hydroxyvitamin D.sub.2 (U.S. Pat. No. 3,585,221), 1.alpha.,25-dihydroxyvitamin D.sub.2 (U.S. Pat. No. 3,880,894), the 24-hydroxy- and 24,25-hydroxyvitamin D.sub.2 metabolites (Jones et al., Arch. Biochem. Biophys. 202, 450 (1980), 1.alpha.-hydroxyvitamin D.sub.2 (U.S. Pat. No. 3,907,843), as well as certain related 22-trans-dehydro compounds lacking the 24-methyl substituent as described in U.S. Pat. No. 3,786,062 and by Bogoslovskii et al. (J. Gen. Chem. USSR 48(4), 828 (1978); Chem. Abstr. 89, 163848j, 89, 209016s).